This invention concerns air filtration such as is used in HVAC and industrial air filtration and dust collection systems.
High efficiency filters remove a large proportion of contaminants, but will quickly become clogged due to buildup of the contaminants on the filter media since a great proportion of the contaminants in the air flow will be filtered out.
Much labor would be required to keep such filters clear by manual removal of the build up of contaminants captured by the filter media.
For this reason, disposable or cleanable prefilters are often used to remove the larger contaminants from the air stream in order to reduce the servicing requirements for the more costly high efficiency filters. However, the inclusion of additional prefilters will add to the maintenance costs of the system.
Self-cleaning air filters are well known which typically carry out cleaning by establishing a reverse air flow through the filter media to dislodge the contaminants, and collecting these contaminants in a lower space which is accessible for periodic disposal of the collected contents.
In this arrangement, dislodged contaminants may be suspended in the air just upstream of the filter media, and can be drawn back onto the filter media when normal operation is restarted.
In another arrangement, a sustained reverse flow can be established which is directed to an exhaust port to thereby make sure that the contaminants are not recaptured by the normal air flow after the reverse flow ceases.
This approach interrupts normal air flow for a significant time and requires a substantial volume of reverse flow through the filter media and a purging flow through the space just upstream of the filter media.
It is also known to periodically direct a brief reverse flow to dislodge the contaminants from the filter media, which it is hoped will settle out and be received in a collection space. This approach minimizes the interruption of normal operation, but is even more likely to result in dislodged contaminants being drawn to the filter media after normal flow through the filter is restored as described above, since only a brief reverse flow occurs, and all of the contaminants will likely not have a chance to settle out away from the filter media before restarting normal air flow.
It is an object of the present invention to provide a self-cleaning air filtration system which will minimize the interruption of the normal air flow in the system while insuring a rapid and substantially complete removal of dislodged contaminants.